Development of high performance dielectric materials is required to facilitate the trend towards miniaturization of microwave communications circuits. A novel two-step sintering process has been found that enhances the value of (Q-factor) (frequency) (QF)product of Ba(Mg ⅓ Ta ⅔)O3 (BMT). Detailed examination of samples densified in this way gives not only details of the grain size, defect content and state of order of the ordered perovskite grains but also reveals the presence of a number of previously unreported phases. These new phases have been examined by TEM using energy dispersive X-ray analysis to give them approximate chemical composition and convergent beam electron diffraction to determine their crystallography. Large unit cells are found which are evidently related to compounds studied previously in the x 3 BaMnO - system. The results will be discussed in relation to the enhanced performance of the materials.